1. Field of the Invention
The invention concerns a process for producing blanks or molded bodies with similar characteristics as wood from one or more cellulose-containing, fibrous raw material, e.g. pure cellulose, but also crude fibers or the complete plant or other constituents of hemp, flax, reed, cotton, straw, etc., as well as old cardboard and waste paper, through specific processing of said fibers to form a microfiber pulp which is then dried, if necessary after first draining and forming it, as well as the diverse use of said microfiber pulp as bonding or matrix material for taking up filler materials.
The objective is an economical production of the aforementioned materials, bodies and molded parts having good technical properties, if possible based on ecological criteria.
2. Description of the Related Art
In the patents CH 254243, DE 4207233 A1, EP 402866 A2, U.S. Pat. No. 3,935,924 A, as well as GB 2066145 A, it is suggested using beaten cellulose or microcellulose pulp as bonding agent, filter, speaker membrane or as thickening and reinforcing agent for paper products. These patents appear to oppose individual claims of the patent under consideration. The process suggested in the CH 254243, however, requires extremely long, uneconomical processing times and the resulting, gelatinous slime has a consistency that makes the drainage of water very difficult. In addition, higher densities and strength can be obtained with this process only by using pressure (at least 4 kg/cm2) and heat (above 100xc2x0 C.).
Basically, considerably lower strengths are achieved on the basis of this Swiss patent and other already known processes than with our process.
Thus, according to the DE 4207233 A1, waste paper is beaten and stirred and, following the introduction of air, is dried to filtering bodies with low strength. It is significant that the inventor considers it necessary to admix the fiber pulp with calcium oxide powder, as is mentioned several times in this patent, in order to obtain firmness and stability for the filter block through a post-curing. The introduction of air into the fiber pulp thus refers to an obviously hardly processed base material with extremely low bonding properties.
The word xe2x80x9cmicrocellulosexe2x80x9d by itself generally does not define either the degree of shortening, squeezing, fibril removal, hydration or the adjusted fractional composition of the fibers, which are critical for the internal cross-linkage, matting and bonding properties.
It is significant that the EP 402866 A2 also does not address the fineness via these bonding properties, but via the filtering characteristics of the material, that is to say whether the material is adjusted finely enough to prevent certain particles (e.g. bacteria and the like) from passing through the filter.
The fact that the use of polymers as raw material is also suggested for these filters, in the cited examples as well as the claims, serves as further proof that the refinement function has another purpose as well as has a very different qualitative and quantitative cause. Thus, the processing clearly does not serve to increase the hydrogen bonding between fibers.
The U.S. Pat. No. 3,935,924 A appears to deal only with carbon-fiber reinforced fine paper with somewhat increased bonding properties for speaker membrane production.
All the aforementioned patents use only pure cellulose, but not cheap crude fibers or other plant constituents. Refiners are used only for shortening of cellulose fibers to make these suitable for further processing, e.g. in a xe2x80x9chigh pressure homogenizer.xe2x80x9d This high-pressure pulping in an expansion nozzle results in totally different fractional compositions and defibration degrees. The same is true for the GB 2066145 A. The pulp produced with this process has considerably lower bonding properties. It is significant that the suggestion is only for using this pulp as reinforcement for paper, but not for the bonding of wood replacement products such as furniture panels or, following the drying, as synthetic material replacement. Adding approximately 40% highly processed micro pulp, produced according to our process, as suggested in table IX of this patent specification, provides the paper with the properties of wood veneer, which is too hard for paper, is brittle and unusable in this function. The conclusion can be drawn from this as well that substantial differences to the present patent exist.
In contrast to the processes suggested in said patents, the process in the present patent permits an economical realization for the intended applications. This concerns the processing expenditure as well as the options for the raw material selection, the drainage times and the suggested processing paths for a product realization. Beyond that, the microfiber pulp produced with this process results in work pieces with higher strength values, which can surpass those of hardwood, without having to use bonding and flux agents or external pressures, given a suitable raw material selection and corresponding processing. Specific gravities of up to 1.5 can be achieved in this way. The light-weight and porous variants also have excellent strength values.
This is achieved through a continuous grinding, chopping and defibration of the cellulose fiber or cellulose-containing fiber in the refiner, wherein a total energy expenditure of at least 0.5 kWh/kg, but ideally 2-2.5 kWh/kg are necessary with a laboratory refiner RO-Escherwys. (In order to determine the actual grinding capacity, the no-load capacity must be deducted from the total energy consumption. Thus, a different ratio between no-load capacity to grinding capacity results if machines with a higher capacity or other suitable fiber chopping and defibration machines are used, and the above-defined total energy consumption must be adapted accordingly.) In this way, a moldable microfiber pulp with very diverse fiber lengths and the tiniest fibril sizes develops, which pulp has the characteristic of hardening to form an ecological, subsequently deformable fiber material with high density (up to a specific gravity of 1.5) and strength without the admixture of adhesives or chemical additives and without the use of pressure, simply through drying and the associated shrinkage.
External pressures and forces applied after the grinding above all serve to effect a quick preliminary drainage, the forming and holding of the form and do not represent a premise for achieving high material strengths. Furthermore, the strengths and densities of the material, as well as the structural fiber arrangements of the work pieces are controlled by varying the raw fiber material used, the amounts of grinding energy and the selected grinding tools, but also the processes used for the prior drainage, forming and drying.
Strength, hardness and formability of the material increase with increasing refinement of the cellulose fiber structure. However, if the fibers are chopped to be extremely small, the strength can be further increased through reinforcement with longer fibers (addition of preferably less than 15% dry substance). The highest strengths can be achieved with an extremely fine-ground microfiber pulp, which is reinforced with a thin net of fibers with varied lengths in a balanced fiber-length distribution. In this case, the extremely fine-ground microfiber pulp provides good bondingxe2x80x94but also good fluxxe2x80x94and thus forming characteristics; the reinforcement distributes the pressure, pull, or shear forces onto larger areas and prevents a short break over a small area.
Processing:
The plastic properties of the microfiber pulp depend directly on its water content.
The microfiber dry substance content between 1-15% is very suitable for pumping into water-permeable forms (step 1). Microfiber pulps with this consistency can also be pressed into rigid, impermeable forms, stamped or rolled. In particular, fiber pulps with higher material density are predestined for these processes (step 2).
The following operational steps can be selected, for example, to produce dimensionally accurate products: step 1; then increasing the material density in the blank or the board through simple drying; subsequently step 2. Depending on the desired dimensional accuracy, this step can also be repeated several times with continued drying in respectively reduced forms that correspond to the shrinkage. Or step 2 and again step 2, as in the above, if necessary also several times. Following respective prior drainage, e.g. in a screen conveyor press or other suitable device, step 2 can be carried out even with very high material densities, depending on the desired form for the work piece, and if necessary a dry substance content of up to 90%.
For hollow bodies, in particular larger hollow bodies, a mandrel is recommended, which is positioned inside the blank and holds the shape during the drying. Housings and containers of any type, from a film container to a furniture piece, can be produced in this way.
The material can also be reshaped after the drying or, following the drying and renewed wetting. Thus, boards or form blanks can be wetted again inside a climate chamber with water-vapor saturated airxe2x80x94possibly also directly in a water bathxe2x80x94in a process lasting several hours or days (depending on the thickness and desired degree of deformation). The material absorbs water during this and becomes plastic, flexible and deformable. With suitable devices, it can be formed, bent, stamped, rolled, blanked, etc.
The shaped body then hardens again through simple drying to the previous density, strength and hardness.
With lower material densities, boards, profile sections and more, as well as batches of these, can be produced in continuous production lines, comprising a prior drainage section and/or subsequent drying section. Extrusion presses that start with higher material densities can also lead to the desired result.
The material weight can be reduced continuously from the specific gravity of the cellulose itself (approximately 1.5) by the inclusion of air or other gas bubbles, but also in general through adding light-weight flux materials. This can be done until a degree of lightness is reached that falls below that of the styrofoam packaging material. The spectrum of density and strength thus extends from values that are approximately those of glass-fiber reinforced synthetic materials to wood-like characteristics (range: between hard tropical wood and balsa wood) and up to the highly porous light-weight materials with good insulating capacity. The inclusion of gas can be achieved through various foaming methods (vortexing or injection of air through nozzles or similar devices), the addition of gasifying agents, through fermenting and more, but also through (partial) blocking of the shrinkage with the aid of reinforcements, through incomplete grinding of the fiber pulp, through freezing methods, excessive heating, etc. The transition from these light-weight materials to the dense hard material is realized continuously here through varying the amountsxe2x80x94and/orxe2x80x94the temperature parameters during the freezing, and if necessary also the drying.
Filler materials can be added by simply mixing them in (best method for low material densities) before or after the grinding, wherein the distribution must be watched carefully, but in any case before the drying is completed. It is possible to obtain varied material characteristics by using the most varied filler materials, which can be included in the basic material matrix of microfibers, but also through the raw material selection. Thus, silicates can be added to inhibit fire; graphite is suitable for increasing the mechanical gliding ability, but also the electrical conductivity; the aesthetic valence can be varied and increased with coloring agents, and the material can be realized to be heavier, lighter, insulating or with high heat conductivity and the like. The desired work piece characteristics are achieved through the quantitative ratio of these material admixtures.
Also, the different quantity shares of plants and fibers used can be processed more or less and parts thereof (those processed more) can function as bonding agents, while others (those less processed) can serve as reinforcement and drainage felt. Strength, specific gravity, insulation value and other technical characteristics are adjusted via the quantity shares, the respective degree of processing as well as the mechanically obtained approximation of the fiber particles prior to the drying.
All these xe2x80x9csecondary materialsxe2x80x9d derived from the microfiber base material, which can be produced through admixtures, raw material selection and process variations in the aforementioned way, are also claimed in the herein presented patent.